This invention relates to improvements in vertical type field effect transistors.
Field effect transistors are preferably small in size and light in weight as far as practicable while having the accuracy as high as possible. Conventional field effect transistors to which the present invention is concerned have included electrodes disposed only on the surface thereof. This has limited the number of electrodes that can be disposed on a field effect transistor. Particularly in integrated circuits, conventional field effect transistors have been scarcely used at high frequencies because interelectrode capacitances increase as distances between electrodes involved become small.
To eliminate these objections, it has been already proposed to embed a semiconductor region with a high impurity concentration in the substrate for field effect transistors thereby to dispose electrodes not only on the surface of the substrate but also in the interior thereof. Conventional field effect transistors having semiconductor regions with high impurity concentration embedded in the substrate therefor have been disadvantageous in that the presence of the capacitance renders the input impedance very low at high frequencies which is attended with a decrease in cut-off frequency. This decrease in input impedance and therefore in cut-off frequency is particularly marked in integrated circuits. Accordingly conventional field effect transistors with embedded semi-conductor regions of high impurity concentration have been scarcely used at high frequencies.